#!/user/bin/env node

const {Readable} = require('stream');

let c = 'a'.charCodeAt(0);

class MyReadable extends Readable{
  constructor(){
    super();
  }

  _read(){
    this.push(String.fromCharCode(c++));
    if(c>'z'.charCodeAt(0)){
      this.push(null);
    }
  }
}

let s = new MyReadable();
s.pipe(process.stdout);
